Manufacture of hot cathodes for electric discharge devices



Patented Mar. 21, 1933 .UNITED STATES PATENT OFFICE" ERICK WIEGAJH), F IBERLIN-WAIDMANNBLUST, GEBmY, ASSIGNOR'TO ELECTRIC COMPANY, A CORPORATION OF NEW YORK MANUFACTURE OF HOT CATHODES ELECTRIC DISCHARGE DEVICES Ho Drawing. Application filed February 11-, 1932, Serial No. 592,450, and in Germany February 14, 1881.

The present invention relates to hot cathodes for electric discharge devices. One of the objects ofn'the invention is to provide a process for thelproduction of a homogeneous alkaline earth lloy suitable for use as'a hot cathode in electrlc discharge devices. A further object of the invention is to provide a cathode structure having a high emission capacity and a relatively long life. Other objects will appear hereinafter.

,Heretofore it has been proposed to employ metals of the alkaline earth group, particularly barium, directly as emission bodies. Since barium melts at about 650 C. and also vaporizes very easily it "can be employed only in the form of a coating on metals of hi h, melting point or as an alloy with suchmeta s. Thus it is known, for example, that metals, like platinum, that form alloys with barium,- can be superficially alloyed with barium by heating in barium vapor, and, in some cases,

after oxidizin a part of the barium metal contained in t e alloy, thesebodies may be employed as cathodes. Gathodes produced in this way have, however, the disadvantage that the alkaline earth metal content is consumed comparatively quickly as generally only a thin superficial layer contains the act1ve metal.

Efi'ortsto produce a homogeneous alkaline earth alloy useful for hot cathodes have heretofore been unsuccessful. This has been due partly to the fact that melts of the two constituents can be produced only with great difficulty since barium metal va orizes very easily. Also it has been-found t at it, is not possible to obtain a homogeneous alloy by causing barium metal in the form of a liquid or a vapor to act on solid bodies of metals of high melting point, because thealkaline earth metal penetrates only very slowly into the deeper layers. Y

' I have discovered that barium metal in a 5 molten condition wets metallic bodies extremely readily and use) is made 'of this property in the production of alkaline earth arium a 'porous metal alloys according to the lpresent invention. If H one treats with molten body such as maybe very easil produced by pressing metal powder suita le apparatus,

. mixed together and b useful cathodes.

The barium content of the alloy produced according to the new process is generally determined by the volume of the pores of the body of the metal of high melting point. By

and to produce a sintering treatment of. the metal body before the alloying action, the volume of the pores can be altered considerably, and in this way alloys with different alkaline earth content can be prepared without difiiculty.

The. alloyed rods can be worked up in a known manner into wire-shaped or stripshaped' cathodes. In doing this it is desirable to anneal the impregnated metal bodies from time to time in a vacuum or in a'rare gas atmosphere. Such cathodes can be made without difliculty from, for example, alloys ofbarium with nickel or platinum having a barium content up to about 10%. with still higher barium content .can pared mechanically The resent process-can be applied also with a vantage in producing in a simple manner very uniform mixtures of barium be prewith metals thatdo not form alloys therewith, as tungsten, molybdenum, tantalum, etc. Subh metal bodies, if their barium con-. tent is not too great may be worked u mechanically without difliculty and emp pyed for cathodic purposes'with good results. Fi-

but only with difiiculty.

Alloys 4 nally, instead of pure barium, easily fusible alloys as barium aluminum bari copper etc. ca n be caused to act on the mu porous metal bodies and the electrical and mechanical properties of the metal bodies can'thus be consideralilw improved.

For many purposes it is advantageous to treat the porous metal bodies in a stream of "porous body and impregnating said with molten barium.

. not be produced.

alkaline earth metal vapor rather than with healing said impregnated body at'intervals molten metal. Whenthus' treated, alloys during the working process.

with more than 5% of barium generally can- However, alloys prepared in this way are characterized by great purity. As by far the greatest proportion of barium compounds are less fusible than barium, in thisprocess only pure barium can enter into the metal bodies.

Cathodes prepared according to the described process can be employed either directly in discharge tubes with or without gas filling or after they have been coated in known manner with alkaline earth oxides. The cathodes are distinguished by a high emission capacity and long duration. I What I claim as new and desire to secure by Letters Patent of the United States, is: 1 The process of producing a metallic structure suitable for use as a hot cathode which comprises pressing apowdered metal of high melting point thereby to provide a body lkawith molten material comprisingan a line earth metal.

2. The process of producing a metallic structure suitable for use asa hot cathode which comprises pressing a powdered metal of high melting point thereby to provide a porous body and. impregnating said body 3. The process I of producing a metallic structure suitable for use as a hot cathode which comprises pressing powdered nickel into a desired shape to thereby provide a porous body and impregnating said porous body with molten barium.

4. The process of producinga metallic structure suitable for use as a hot cathode whichcomp'rises pressing a powdered metal of high melting point therebyto provide a porous body, impregnating said porous body with molten material comprising an alkaline earth metal and heating said impregnated body thereby to form an alloy of said metal with at least a portion of said alkaline earth metal.

5. The process of producing a metallic structure suitable for use as a hot cathode which comprises pressing "a powdered metal ofihigh melting point in a mold, impregnating said powdered metal with molten barium, mechanically working the impregnated body into a'desired shape and annealing said impregnated body at intervals during the working process.

6. The process of producing a metallic structure suitable for use as ahot cathode In witness my hand.

which comprises pressing powdered. high melting point metal in. a mold, partially sintering said pressed material to thereby control its orosity, impregnating said partially cintere material with a molten alkaline earthmetal, mechanically working the impregnated body into a desired shape and-anwhereof, I have hereunto set ERICH WI GAND. 

